Cables, belts, and straps are utilized as tensional elements in bracing systems found in aircraft, boats, cranes, winches, bridges and various other mobile and static structures such as buildings and signage structures. Naturally, light weight assemblies of cables and connecting elements are typically preferred in order both to save expenses in their constructions and to maximize payload capabilities of a structure. Compact assemblies are typically preferred in order to maximize the useful space within a structure and in order to minimize the overall size of a structure. Compact assemblies are also typically preferred where cables and connecting elements are exposed and are subject to fluid forces. Fluid forces such as the air resistance forces encountered by vehicles such as aircraft and boats may result in higher fuel expenses and shorter travel ranges. Fluid forces such as wind loads may affect the stability of structures such as bridges and may therefore increase construction costs and adversely affect longevity.
With some assemblies having tensioned cables, the weakest portions of the assemblies are found where cables couple to connecting elements. Forces transverse to the longitudinal axes of cables are often introduced at couplings and connections by clamps, crimps, and other connecting means. Transverse forces that tend to compress or flatten a cable can compromise the effective tensional strength of the cable. Such compromising transverse forces may be of concern when using even time-honored materials such as steel cables, but are often of heightened concern when using modern fibers.
Some classes of modern synthetic fibers provide the advantages of low weights relative to metal cables having similar tensile strengths. Examples of modern synthetic fibers include DuPont's Kevlar (™) and Teijin's Technora (™). Some examples of synthetic fibers are spun in slender fibers and are grouped together to form yarns which are further grouped to form cables and other tensionable assemblies. The molecular structure of some typical such fibers provide impressive tensile strength along their lengths but are vulnerable to damage and failure when subjected to forces transverse to their lengths such as shear forces and transverse compression forces. Thus, particular care is needed when terminating, coupling, connecting and wrapping some modern yarns, cables, belts and other tensionable assemblies of fibers.
Often a thimble is disposed between a tensioned cable and an anchor in order to inhibit kinking of the cable. For example, a thimble and thimble insert are described in the U.S. Pat. No. 4,398,336 to Beuch, wherein the cable passes about a thimble and is secured thereabout by a swage. A high strength cable of synthetic fibers can be produced by wrapping a synthetic fiber or yarn of fibers multiple times about spaced opposing thimbles such that an elongate fiber assembly extends between the thimbles. A high number of wraps can be achieved so that the load on any fiber or yarn strand is small once the cable is tensioned. The termination of the wrapping can be achieved with friction, with a swage, or with a simple knot. A problem arises, however, when strong cables are needed. As wraps are added to the assembly, thickness is built up as layer upon layer of fibers or yarns are wrapped. When the complete cable is tensioned, relatively inner layers abutting the thimbles are pressed upon by relatively outer layers such that the inner layers are subjected to compression forces. Undesirable damage and even a cascading failure of a cable may result beginning with the failures of inner-most layers.
In order to assure the integrity and durability of a cable, a large cable having superfluous tensional strength along its length can be used and tensions that may challenge a cable at terminations and connections can be minimized or eliminated by careful practice. Such solutions, however, entail using cables that are heavy and that have large cross-sectional areas. Such solutions are therefore less than optimal and, in a sense, defeat many of the very goals underlying the development of modern fibers which were developed to be lightweight and compact.
A need exists for improvements in cable terminations and connectors. A need exists for compact devices for coupling cables to structures. A need exists for improved cable terminations and connectors that exploit the tensional strengths of fiber assemblies and that protect fiber assemblies from the vulnerabilities of modern fibers with regard to shear forces and transverse compressions.